Conventionally, coated tools are known, such as a cutting tool in which one or multiple coating layers such as titanium carbide layers, titanium nitride layers, titanium carbonitride layers, aluminum oxide layers, and titanium nitride aluminum layers are formed on the surface of a base material such as a cemented carbide, a cermet, a ceramic material or the like.
The occasions where the cutting tool is used for heavy-load intermittent cutting in which a large impact is applied to a cutting edge or the like are increased with the recent increase in the efficiency of cutting processing. Under such severe cutting conditions, a large impact is applied to the coating layer, and chipping or the detachment of a coating layer tends to occur. Thus, the improvement in fracture resistance of the coating layer has been demanded for preventing the occurrence of chipping or the detachment of the coating layer.
As a technique for improving fracture resistance in a cutting tool as mentioned above, Patent Document 1 discloses a technique whereby it becomes possible to optimize the grain diameters and the layer thickness of an aluminum oxide layer and to adjust the texture coefficient on face (012) to 1.3 or more to form an aluminum oxide layer that is dense and has high fracture resistance. Patent Document 2 discloses a technique whereby it becomes possible to adjust the texture coefficient on face (012) in an aluminum oxide layer to 2.5 or more to make the residual stress in the aluminum oxide layer to be released easily, thereby improving the fracture resistance of the aluminum oxide layer.
As a technique for improving wear resistance of a cutting tool as mentioned above, Patent Document 3 discloses a technique whereby it becomes possible to improve strength and toughness of a coating film by forming an aluminum oxide layer located immediately above an intermediate layer by laminating at least two unit layers having different X-ray diffraction patterns from each other to form the aluminum oxide layer.
Patent Document 4 discloses a cutting tool in which the texture coefficient on face (006) in an aluminum oxide layer is increased to 1.8 or more and the peak intensity ratio I(104)/I(110) between the peak intensity on face (104) and the peak intensity on face (110) is adjusted to a value falling within a specific range.
Patent Document 5 discloses a cutting tool in which the peak intensity ratio I(104)/I(012) between the peak intensity on face (104) and the peak intensity on face (012) in an aluminum oxide layer is adjusted in such a manner that the peak intensity ratio in a first surface of the aluminum oxide layer is larger than that in a second surface of the aluminum oxide layer.
In the cutting tools described in Patent Documents 1 to 5, however, higher wear resistance and fracture resistance of the coating layers are demanded. Particularly, it is demanded to prevent fine chipping that is likely to occur in an aluminum oxide layer, and prevent wearing that is likely to progress easily by the fine chipping, and thereby further improve the wear resistance of the aluminum oxide layer.